The 'poll' example in section 2.6 shows the submitInfo attribute value holding the ID of a 'model' element whereas the intent would seem to be that this should hold the ID of a 'submitInfo' element inside some 'model' element. The example earlier in section 2 does show it this other way.
In some cases you have explicitly added a sentence declaring it to be an error where, for example, the IDREF value in a 'model' attribute is the ID of an element other than a 'model' element.
Do you want to pull that out as a separate sentence as regards this submitInfo linkage?
Isn't there a way to get this kind of a constraint into the schema?
Al